https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99457
Bug ID: 99457
Summary: gcc/gdb -gstabs+ is buggy.
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: jay.krell at cornell dot edu
Target Milestone: ---
gcc/gdb -gstabs+ is buggy.
Could be either, I didn't investigate.
The codegen is correct.
That's ok, I didn't really need it, I'll use regular -g.
$ cat 1.c
#include <stdio.h>
int main()
{
char a[100] = {0};
printf("%d\n", a[0]);
}
$ gcc --version
gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0
$ gcc -gstabs+ 1.c
# correct output
$ ./a.out
0
$ gdb --version
GNU gdb (Ubuntu 9.1-0ubuntu1) 9.1
$ gdb ./a.out
(gdb) break main
(gdb) r
Breakpoint 1, main () at 1.c:3
3 {
(gdb) n
4 char a[100] = {0};
(gdb)
5 printf("%d\n", a[0]);
(gdb) p a
$1 =
"@\003\000\000@\003\000\000@\003\000\000@\003\000\000@\003\000\000@\003\000\000@\003\000\000@\003\000\000@\003\000\000@\003",
'\000' <repeats 11 times>, "\001", '\000' <repeats 49 times>
(gdb) p a[0]
$2 = 64 '@'
(gdb) disas
Dump of assembler code for function main:
0x0000555555555169 <+0>: endbr64
0x000055555555516d <+4>: push %rbp
0x000055555555516e <+5>: mov %rsp,%rbp
0x0000555555555171 <+8>: sub $0x70,%rsp
0x0000555555555175 <+12>: mov %fs:0x28,%rax
0x000055555555517e <+21>: mov %rax,-0x8(%rbp)
0x0000555555555182 <+25>: xor %eax,%eax
0x0000555555555184 <+27>: movq $0x0,-0x70(%rbp)
0x000055555555518c <+35>: movq $0x0,-0x68(%rbp)
0x0000555555555194 <+43>: movq $0x0,-0x60(%rbp)
0x000055555555519c <+51>: movq $0x0,-0x58(%rbp)
0x00005555555551a4 <+59>: movq $0x0,-0x50(%rbp)
0x00005555555551ac <+67>: movq $0x0,-0x48(%rbp)
0x00005555555551b4 <+75>: movq $0x0,-0x40(%rbp)
0x00005555555551bc <+83>: movq $0x0,-0x38(%rbp)
0x00005555555551c4 <+91>: movq $0x0,-0x30(%rbp)
0x00005555555551cc <+99>: movq $0x0,-0x28(%rbp)
0x00005555555551d4 <+107>: movq $0x0,-0x20(%rbp)
0x00005555555551dc <+115>: movq $0x0,-0x18(%rbp)
0x00005555555551e4 <+123>: movl $0x0,-0x10(%rbp)
=> 0x00005555555551eb <+130>: movzbl -0x70(%rbp),%eax
0x00005555555551ef <+134>: movsbl %al,%eax
0x00005555555551f2 <+137>: mov %eax,%esi
0x00005555555551f4 <+139>: lea 0xe09(%rip),%rdi # 0x555555556004
0x00005555555551fb <+146>: mov $0x0,%eax
0x0000555555555200 <+151>: callq 0x555555555070 <printf@plt>
0x0000555555555205 <+156>: mov $0x0,%eax
0x000055555555520a <+161>: mov -0x8(%rbp),%rdx
(gdb) q
$ gcc -g 1.c
$ gdb ./a.out
(gdb) r
Breakpoint 1, main () at 1.c:3
3 {
(gdb) n
4 char a[100] = {0};
(gdb)
5 printf("%d\n", a[0]);
(gdb) p a
$1 = '\000' <repeats 99 times>
